A wasteful struct - are you kidding?

I'm not. Is there some performance penalty for using a struct over a 2 element array?

No performance penalty. It would make the code longer.

Consider "<Foo> in <bar> lines" type articles to be performance pieces - the point is to make it short, not readable or user friendly.

In this case, it makes no difference. The array is used instead of a struct to save a few lines of code and making the title of this post more impressive.